I. Field of the Invention
This invention relates to computer-aided design (CAD) systems and, in particular, to a system and method for providing dimensionally correct mapping of two-dimensional ("2-D") surface detail to a three-dimensional ("3-D") surface in a design system in order to eliminate distortion found in prior known systems. The present invention has specific applications to the apparel, footwear, furniture, automotive or interior design industries.
II. Description of the Prior Art
In the field of computer-aided design, one of the objectives is to display a realistic image of the object displayed on the graphic visual output device, e.g., the cathode ray terminal ("CRT") of the system. A method for enhancing the realism of the displayed image of the object is the addition of detail to the surfaces making up the object using texture mapping techniques. Such texture mapping techniques have been employed in other 3-D CAD systems, notably those used in making computer-generated animated films. The objects designed on and displayed by such systems are represented internally as surface data structures that reflect the 3-D topology of the object. The texture mapping algorithms incorporated into those systems use that topology as a guide for applying the texture over the surfaces making up the object displayed. The two major steps in performing texture mapping are computing the map, and displaying the mapped image. Computing the mapping typically involves a transformation from the 2-D coordinate space of the texture to the coordinate system defined over the 3-D surface, typically a 2-D parameterization of the surface function, which implicitly defines the map to the 3-D surface itself. See Procedural Elements for Computer Graphics by David F. Rogers, pp. 354-363 (Mcgraw-Hill 1985) and "Survey of Texture Mapping" by Paul S. Heckbert, pp. 321-332, Tutorial: Computer Graphics: Image Synthesis, K. Joy, C. Grant, N. Max, and L. Hatfield eds., (IEEE Computer Society Press 1988). These .references give thorough discussion to the problem of displaying the mapped image, which involves, once the map is performed, transforming the texture information from the 3-D object space to the 2-D screen space. Issues covered in the references center around the transformation to screen space and filtering the texture to reduce aliasing (jagged) artifacts in the final image. The mapping function may also be defined differently. For example, rather than mapping to a 2-D parameterization defined on a surface, a ,solid texture, function may be defined for every 3-D point through which a surface passes. This is very effective for simulating objects carved from such materials as wood and marble. See "Solid Texturing of Complex Surfaces" by Darwyn R. Peachy, and "An Image Synthesizer" by Ken Perlin, both in Computer Graphics, Vol. 19, Number 3, Proceedings of SIGGRAPH (Association for Computing Machinery 1985), pp. 279-296.
By way of example, in the apparel industry a pattern piece for a part of a garment designed on a CAD system may be represented by a 3-D mathematical surface, typically a parametric spline surface that exhibits an inherent 2-D parameterization. As outlined in the above references, conventional texture mapping algorithms would exhibit a linear mapping from the (u,v) orthogonal coordinate system of the texture to the (s,t) orthogonal coordinate system inherent in the parametric spline surface. The texture mapped, then would consist of a strictly rectangular block of the texture image distorted and projected onto the surface. A technique for flattening 3-D surfaces into 2-D pattern pieces in a 3-D CAD system with applications to soft goods industries is disclosed in U.S. Pat. No.. 5,107,444 issued Apr. 21, 1992 assignee's co-pending U.S. patent application Ser. No. 07/243,616 entitled "Method And Apparatus For Flattening Three-Dimensional Surfaces" (Chien Tai Wu) incorporated by reference herein. This application discloses a system in which a 3-D surface, representing a pattern piece for apparel, footwear, upholstery, or any other soft goods article composed of sheets of flexible material, may be flattened to a 2-D representation of the outline needed for the cutting the pattern piece from a larger sheet of material. In other words, the 3-D surface representation is "unfolded" to a flat 2-D representation It is the relationship between a 3-D surface and its corresponding 2-D flattened pattern piece that the present invention uses to generate a realistically mapped image. Any situation where this relationship exists is suitable for use with the current invention. A situation where there may be a 3-D surface to 2-D flattened piece relationship may be where a 2-D piece is deformed into a 3-D ruled surface with the same surface area. Another possibility is described in "The Synthesis of Cloth Objects" by Jerry Weil in Computer Graphics, Vol. 20, Number 4, Proceedings of SIGGRAPH (Association for Computing Machinery 1986), pp.49-54, where a 2-D piece of cloth may be deformed using a computer simulation in 3-D to display the `drape` of a piece of cloth. In this case, the draping simulation based on a given flat pattern shape will yield a 3-D mesh of points, through which an interpolating 3-D parametric surface may be fit. In these cases we still have the relationship between the 3-D surface and the 2-D flattened pattern piece cut from a flexible sheet of material, all of which may be used in conjunction with the current invention.
If the sheet of material is a textile, the image of that textile may be captured digitally and stored in a computer using well-known scanning methods, and this bitmap image may then be used as the 2-D bitmap image for the texture mapping. Traditional texture-mapping methods would only display a precise 3-D mapped image of the object when the flattened pattern piece of the 3-D surface is perfectly rectangular. Such methods are inadequate for the general case of 3-D pattern pieces with non-rectangular flattened pattern shapes.